An embodiment of this disclosure relates to the voltage generator of a nonvolatile memory device and, more particularly, to the voltage generator of a nonvolatile memory device which is capable of reducing an area.
Recently, there is an increasing demand for a nonvolatile memory device which enables electrical program and erasure and does not perform a refresh operation of rewriting data every specific interval to prevent loss of data.
In the nonvolatile memory device, a program voltage, an erase voltage, and a read voltage are supplied to word lines in order to store specific data in a memory cell array. These voltages are generally supplied by a voltage generator.
A known voltage generator includes a regulator configured to output a pumping voltage by operating a charge pump according to a specific clock cycle and stabilizing the pumping voltage in a constant level. In this construction, when the pumping voltage becomes a constant level or higher, the operation of the charge pump is stopped.
FIG. 1 is a circuit diagram showing a voltage generator having a double regulator structure.
Referring to FIG. 1, the voltage generator 10 includes an oscillator 11, a pump 12, and first to third regulators 13 to 15.
The oscillator 11 generates a clock CLK having a constant cycle. The pump 12 generates a pump output voltage PUMPOUT in response to the clock CLK. The first regulator 13 compares a voltage Va, divided from the pump output voltage PUMPOUT, with a first reference voltage VBG to output a first comparison signal CS1 according to a result of the comparison. The first comparison signal CS1 controls the output operation of the oscillator 11. That is, when the pump output voltage PUMPOUT becomes a set level or higher, the first regulator 13 stops the output operation of the oscillator 11. Accordingly, the pump output voltage PUMPOUT generated from the pump 12 may not increase. The second and the third regulators 14 and 15 generate first and second regulation voltages VREG1 and VREG2 having different levels, respectively, by dividing the pump output voltage PUMPOUT.
The above-described voltage generator having a double regulator structure has an excellent power supply rejection ratio (PSRR), because the first regulator 13 maintains the pump output voltage PUMPOUT regularly. The voltage generator with a double regulator structure less affects a distribution of the threshold voltages of the memory cells of a nonvolatile memory device, because the first and the second regulation voltages VREG1 and VREG2 generated from the second and the third regulators 14 and 15 have a small ripple.
In the above-described voltage generator having a double regulator structure, the plurality of regulators consumes an amount of current because current paths Current1 to Current5 due to a number of the regulators increase. Furthermore, if the type of voltages used in a nonvolatile memory device increases, the number of regulators also increases, thereby further increasing current paths.
In order to solve the concerns, a nonvolatile memory device includes not only the above-described voltage generator having a double regulator structure but a voltage generator including a single regulator structure for a high level voltage.
FIG. 2 is a circuit diagram showing a voltage generator having a single regulator structure.
Referring to FIG. 2, the voltage generator 20 having a single regulator structure includes a first voltage generator 21 for generating a first regulation voltage VREG1 and a second voltage generator 22 for generating a second regulation voltage VREG2.
The first voltage generator 21 stabilizes voltage generated from a pump 21B, using a regulator 21C, and generates the first regulation voltage VREG1 having the stabilized voltage. The second voltage generator 22 has a similar structure and operation to the first voltage generator 21.
The voltage generator 20 having a single regulator structure has low current consumption, because it the number of current paths is smaller than that of the voltage generator 10 having a double regulator structure. However, the voltage generator 20 with a single regulator structure has an adverse effect on the PSRR, because the source power of the pump has a great ripple always. Accordingly, a ripple is generated in the outputted first and the second regulation voltages VREG1 and VREG2. As a result, a distribution of the threshold voltages of memory cells is widened by operating voltages used in a nonvolatile memory device. Furthermore, a time gap between the time for rising a level of the first regulation voltage VREG1 in the first voltage generator 21 and the time for outputting a level of the second regulation voltage VREG2 in the second voltage generator 22 is generated based on different loads, because the first and the second voltage generators 21 and 22 have different power sources. Accordingly, the time taken for the first regulation voltage VREG1 to be generated may differ from the time tame taken for the second regulation voltage VREG2 to be generated.
The known nonvolatile memory device includes both the voltage generator having a double regulator structure and the voltage generator having a single regulator structure. If device characteristics are deteriorated because a distribution of the threshold voltages of memory cells is widened by the voltage generator having a single regulator structure, the voltage generator having a double regulator structure is used instead of the voltage generator having a single regulator structure. As a result, there are concerns about an integration degree because voltage generators occupy a very large area in a nonvolatile memory device. Current consumption is large although the voltage generator having the double regulator structure is used.